The present invention relates to a wash arm construction.
A typical dishwasher includes one or more elongated wash arms which rotate about a vertical axis located at their longitudinal midpoint. Each arm is hollow and includes a plurality of apertures spaced apart from one another along the length of the arm. Pressurized cleaning fluid or water is introduced to the cavity within the arm, and is sprayed outwardly through the various spray apertures along the length of the arm.
During rotation of the arm, the distance a particular spray hole in the arm travels increases significantly the further its distance from the center of rotation. Because the travel distance increases farther away from the rotational center of the arm, the velocity of the spray holes at various locations on the arm is also significantly different, with the greater speeds being farther from the rotational axis of the arm. Therefore, a jet of washing fluid from a spray hole at the end of the arm impacts a dish for a much shorter period of time than a jet from a spray hole nearer to the center of the arm. In order to get sufficient washing fluid to the dishes located adjacent the outer end of the arm, the fluid pressure in the arm must be fairly high to achieve good washing performance. If this high pressure is used, the spray holes located closer to the pivotal axis of the arm are allowed to create sprays which impact dishes for a long enough period of time to cause the dishes to move. Dish movement frequently occurs near the center of the pivotal axis in prior art machines.
In many dishwashers, the dishes which are most likely to be moved by high pressure spray are generally located in the area which is approximately half way between the pivotal axis of the arm and the outer end of the arm. Therefore, it is desirable to provide a spray arm which has the capability of varying the pressures at the various spray holes so as to decrease the pressures in the areas where the fluid jets are likely to impact and move a dish. Reducing the fluid pressure in these areas minimizes dish movement while still maintaining the higher pressures at the outer ends of the arm where needed.